Boyfriend is insecure about penis size, help

My boyfriend is the perfect lover imo, he's seriously stellar in bed. Buuut he "jokes" a lot about having a small penis or how he doesn't think he's attractive enough. I seriously cannot fathom how he could think that, he's basically a sex god. That man has powers, I swear. I try to make him understand that I love our sex life and am very satisfied, and if he's not that okay we can add/remove things and make it better for him. He kind of dismisses me with another self deprecating joke and doesn't say anything about it for a while.

How do I show him how perfect he is? I don't get how he doesn't see it. He's really not small either, he has plenty of girth and is something like seven inches, I haven't measured lol